The mammalian cochlea responds to sound stimuli with remarkable sensitivity by a mechanical amplification process (termed cochlear amplification) that resides in the cochlea's outer hair cells (OHCs). The change of OHC soma length driven by transmembrane voltage (termed OHC electromotility) has been hypothesized to provide mechanical feedback and, thereby, cochlear amplification. A complex of molecules within the lateral wall of OHCs (termed the motor complex) is thought to be responsible for OHC electromotility. In this proposal, we focus on the genetic analysis of the mechanism underlying OHC electromotility and cochlear amplification in mice. Using a knockout mouse, we have provided evidence that prestin, a recently discovered protein in the plasma membrane of the motor complex, is required for OHC electromotility and cochlear amplification. To further elucidate the molecular basis of OHC electromotility and its role in cochlear amplification, we plan to determine: 1. whether prestin-mediated OHC electromotility is the only active mechanism in OHCs to generate cochlear amplification. 2. how prestin-mediated OHC electromotility provides feedback for cochlear amplification; and 3. how other molecules of the motor complex in the OHC's lateral wall contribute to prestin-mediated OHC electromotility and, thereby, cochlear amplification. Biochemical, physiologic, and genetic analyses of mutant mice will enable us to elucidate the molecular pathway that underlies OHC electromotility and cochlear amplification. Our studies may provide insights into the mechanisms by which hearing loss involving deficiencies in OHC electromotility occurs in humans.